The present invention relates generally to the production of bent sheets or plates of glass and, more particularly, to an improved electrical contact assembly employed in apparatus for forming relatively sharp angled bends in a glass sheet.
In some of the latest automotive designs, it has been found desirable to provide certain of the glazing closures, such as the backlights for example, with sharp bends to form a central panel portion extending continuously across the vehicle from one side to the other thereof, and integral end portions sharply bent inwardly relative to the central panel portion about generally vertical lines to extend longitudinally into the sides of the vehicle.
One successful technique developed for imparting such sharp bends to glass sheets is disclosed in U.S. Pat. Nos. 3,762,903 and 3,762,904, assigned to the same assignee as the present invention, whereby one or more electrically conducting paths are formed on at least one surface of the glass sheet along the line or lines about which it is desired to sharply bend the sheet. The sheet is then supported on a suitable gravity mold structure and heated in a furnace to a temperature corresponding to the softening point of the glass, causing it to sag by gravity into conformance with the shaping surfaces of the mold while simultaneously passing an electric current through the electrically conducting path or paths to heat the area of the glass sheet immediately adjacent said paths to a temperature above the aforementioned softening point, causing the sheet to bend along such path or paths to form the desired relatively sharp bends therein. Incorporating such a procedure in a fully automated, mass production operation poses problems in satisfactorily supplying and introducing the electric current to the electrically conducting paths on the glass sheets. A particularly critical problem in maintaining electrical continuity resides in the electrical contacts which make electrical connection with the paths or conducting lines on the glass sheet.
Attempts have been made to solve this problem by employing glass edge contactors mounted on the mold and which are spring biased against opposite edges of the sheet. While these perform satisfactorily, they require the electrically conducting paths to be extended to and along at least portions of the edges of the glass sheet. This is done by manually painting the silver-glass frit composition forming the paths along such edges after the automatic silk screen printing operation. Not only does this additional manual step add materially to production costs, but it also yields varying thicknesses of the composition applied, which tends to vary the electrical characteristics from sheet to sheet. Moreover, in the bending of glazing closures by the gravity mold technique, portions of the glass sheet move relative to the shaping surface of the mold as it sags from its flat condition to the final bent condition. This creates frictional movement between the contacts and the glass sheet edge, tending to scrape off the frit composition to produce conductor line burn outs. Also, this abrasive action causes the contacts to deteriorate, resulting in frequent contact replacement. Also, in the production of certain deep, sharply bent glazing closures, the relative movement between the glass sheet and the mold is great enough to cause the contacts to completely disengage or slide off the glass sheet edges.
Other attempts employing a top surface contact have not been entirely satisfactory because the severe rocking and turbulent advancement of the mold through a furnace induces vibrations in the top surface contacts, resulting in variations of contact pressure with attendant line burn out. Also, some of the silver-glass frit composition tends to fuse to and build up on the contacts formed of conventional materials, also causing burn outs.